The purpose of this project has been twofold: (1) to study the effects of argon laser photocoagulation as a therapeutic modality in certain retinal and choroidal vascular diseases, including background and proliferative diabetic retinopathy, retinal vein occlusion, sickle cell retinopathy, senile macular degeneration, the presumed ocular histoplasmosis syndrome, and idiopathic detachments of the retinal pigment epithelium. Eyes to be treated are selected randomly from eyes in each disease category judged eligible for treatment according to specific criteria. Untreated eyes serve as controls and document the natural history of these diseases. Treated and untreated eyes are evaluated on the basis of visual acuity, visual fields, electrophysiological parameters and fluorescein angiograms. (2) to study the relationships between systemic levels of certain hematologic factors such as von Willebrand factor, fibrinogen, and hemoglobin A1C, and the rate of aggregation of normal donor platelets in the presence of plasma from test subjects together with adenosine diphosphate, and the presence and severity of retinopathy in individuals with longstanding insulin-dependent diabetes mellitus.